<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
  body > * {
    width: 95%; height: auto; margin: 0 auto; margin-top: 10px;
    border: 1px solid #000; padding: 5px;
  }
  header { height: 50px; }
  section { height: 300px; }
  footer { height: 30px; }
  section > * { height: 100%; border: 1px solid #000; float: left; }
  aside { width: 25%; }
  article { width: 70%; margin-left: 1%; }
</style>

</head>
<body>
    <header>header</header>
    <nav>nav</nav>
    <section>
        <aside>aside</aside>
        <article>article</article>
    </section>
    <footer>footer</footer>
</body>
</html>